Polysiloxane-polyoxyalkylene block copolymers have found wide acceptance as foam stabilizers in the production of polyurethane foam. Such block copolymers include those copolymers whereby the polysiloxane and polyoxyalkylene blocks are linked by hydrolytically unstable silicon-oxygen-carbon bonds which copolymers are often referred to as hydrolyzable polysiloxane-polyoxyalkylene block copolymers, as well as those copolymers whereby said blocks are linked by hydrolytically stable silicon-carbon bonds, which copolymers are often referred to as non-hydrolyzable polysiloxane-polyoxyalkylene block copolymers.
Hydrolyzable polysiloxane-polyoxyalkylene block copolymers can be prepared by a variety of common chemical reactions, e.g. by reacting a linear polyoxyalkylene polymer (polyether) whose linear chain is end blocked at one end by a hydroxyl group and at the other end by an alkoxy, aryloxy, or aralkyloxy group, with a polysiloxane containing a silanic hydrogen, an alkoxy radical, an amino radical, or a halogen atom directly attached to a silicon atom of the polysiloxane, as shown e.g. by the following skeletal equations: EQU .tbd. SiOCH.sub.3 + HOC.tbd. .revreaction..tbd. SiOC.tbd. + CH.sub.3 OH EQU .tbd. SiH+ HOC.tbd. .fwdarw..tbd. SiOC.tbd. + H.sub.2 EQU .tbd. SiCl+ HOC.tbd. .revreaction..tbd. SiOC.tbd. + HCl EQU .tbd. SiN(CH.sub.3).sub.2 + HOC.tbd. .fwdarw..tbd. SiOC.tbd. + HN(CH.sub.3).sub.2
Non-hydrolyzable polysiloxane-polyoxyalkylene block copolymers are usually prepared by the platinum catalyzed addition reaction of a siloxane containing silanic hydrogen with a linear polyoxyalkylene polymer (polyether) whose linear chain is end blocked at one end by an alkenyloxy group (e.g. allyloxy) and at the other end by an alkoxy, aryloxy, aralkyloxy, or an acyloxy group, as shown e.g. by the following skeletal equation: EQU .tbd. SiH+ H.sub.2 C=CHCH.sub.2 OC.tbd. .fwdarw..tbd. SiCH.sub.2 CH.sub.2 CH.sub.2 OC.tbd.
thus, polysiloxane-polyoxyalkylene block copolymers in general are normally prepared by mixing the polysiloxane and polyoxyalkylene reactants in the presence of a solvent and a catalyst, effecting the required chemical reaction, neutralizing the catalyst, removing the solvent, and filtering. Of course, it is understood that reactions which produce a by-product that is in equilibrium with the desired product and reactants must be driven to completion. For example, a compound such as an organic amine may be added to react with the hydrogen chloride produced by the reaction of a polyoxyalkylene alcohol with a chlorosiloxane as shown above, while the methanol produced by the reaction of a polyoxyalkylene alcohol with a methoxy-siloxane as shown above, may be removed by distillation. The employment of a solvent increases the cost of the operation to produce suitable polysiloxane-polyoxyalkylene block copolymer foam stabilizers for polyurethane foam: by reducing the amount of block copolymer that can be prepared per batch in a given reactor; by increasing the time required to prepare a batch of the block copolymer by the time required to remove the solvent; and by adding the cost of the solvent to the raw material cost of the block copolymer. It is quite obviously desirable then to be able to reduce or eliminate the required use of a solvent in the production of suitable polysiloxane-polyoxyalkylene block copolymer foam stabilizers for polyurethane foam.
Moreover, it is also well known that both the polysiloxane blocks and the polyoxyalkylene blocks of polysiloxane-polyoxyalkylene block copolymers employed as foam stabilizing agents for polyurethane foam are comprised of a mixture of molecular species. The polysiloxane blocks (e.g., polydimethylsiloxane) have species distributed by molecular weight, by the number of coupling sites in a molecule and by the position of the coupling sites in a molecule, while polyoxyalkylene blocks (e.g. polyoxyethylene-oxypropylene) have species distributed by molecular weight and by the proportion of ethylene oxide and propylene oxide units within a molecule. The polysiloxane-polyoxyalkylene block copolymers then have polyoxyalkylene blocks representing various molecules in the mixture distributed on different polysiloxane molecules.